Learned odor discrimination in Drosophila without combinatorial odor maps in the antennal lobe.
A unifying feature of mammalian and insect olfactory systems is that olfactory sensory neurons (OSNs) expressing the same unique odorant-receptor gene converge onto the same glomeruli in the brain [1-7]. Most odorants activate a combination of receptors and thus distinct patterns of glomeruli, forming a proposed combinatorial spatial code that could support discrimination between a large number of odorants [8-11]. OSNs also exhibit odor-evoked responses with complex temporal dynamics [11], but the contribution of this activity to behavioral odor discrimination has received little attention [12]. Here, we investigated the importance of spatial encoding in the relatively simple Drosophila antennal lobe. We show that Drosophila can learn to discriminate between two odorants with one functional class of Or83b-expressing OSNs. Furthermore, these flies encode one odorant from a mixture and cross-adapt to odorants that activate the relevant OSN class, demonstrating that they discriminate odorants by using the same OSNs. Lastly, flies with a single class of Or83b-expressing OSNs recognize a specific odorant across a range of concentration, indicating that they encode odorant identity. Therefore, flies can distinguish odorants without discrete spatial codes in the antennal lobe, implying an important role for odorant-evoked temporal dynamics in behavioral odorant discrimination.
DasGupta
Shamik
S
Department of Neurobiology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA.
Waddell
Scott
S
D000818:Animals; D001921:Brain / Q000502:physiology; D004193:Discrimination Learning / Q000502:physiology*; D004330:Drosophila / Q000502:physiology*; D029721:Drosophila Proteins / Q000378:metabolism; D055696:Olfactory Perception / Q000502:physiology*; D018034:Olfactory Receptor Neurons / Q000502:physiology*; D018035:Receptors, Odorant / Q000378:metabolism
D029721:Drosophila Proteins; C492465:Orco protein, Drosophila; D018035:Receptors, Odorant